It is well known that the manufacture of a syringe needle involves the following steps:
(a) A stainless steel pipe conforming to the standard requirements for producing syringe needles is drawn through a die to a specified inner and a specified outer diameter. PA1 (b) A tube thus obtained by the drawing is cut by a grinder to a length appropriate to a syringe needle. This tube is generally called a cut tube. PA1 (c) Burrs developing and sticking on the cut section of this cut tube are removed. PA1 (d) After the burr-removing, said cut tube is washed and dried. PA1 (e) The cut tube is subjected to barrel-grinding to finish the outer surface of the cut tube to a smooth mirror surface and to round off the cut section. PA1 (f) Barrel-grinding is followed by washing and drying, and in consequence a finished cut tube is obtained. PA1 (g) The one end of each cut tube is ground by a grinder to form a main bevel at a specified angle. Next, the both sides of the main bevel are ground to form side bevels, thereby producing syringe needle tube with a piercing point at the tip. PA1 (h) The syringe needle tube is washed and dried. PA1 (i) At the opposite end to the side where the piercing point is formed, a needle base for inserting the syringe needle in an injector is provided and thus a crude syringe needle is obtained. PA1 (j) The crude syringe needle is washed, dried and finally finished to a complete syringe needle.
From the nature of its use, the syringe needle should meet the following requirements: It should be sanitary; it must be safe for use; it must have a low piercing resistance to the human body; and it must offer a low resistance to the blood or the injection liquid flowing through it.
Among others, the sanitary requirement should be strictly fulfilled. Thus, when a random sampling of the mass-produced syringe needles for quality control reveals that the needle is contaminated with foreign matter such as grinder particles, metal powders or even the slightest pollution with dirty cutting oil or a detergent, the whole lot of products will be rejected as failing to meet the sanitary requirements of the syringe needles for human use.
From this standpoint, one of the most important considerations in the conventional manufacture of the syringe needles has been how to prevent the needles from being contaminated with metal powders or, grinder particles deposited inside the tube in the cutting or piercing point-forming step, or with dirty cutting oil or detergent left unflushed, before such tubes reach the market.
The cut tube is obtained by die-drawing a stainless steel pipe to a specified inner and a specified outer diameter and then cutting it to a length appropriate to be used as a syringe needle. Thereby, the drawing process is liable to leave tiny asperities and grooves on the internal tube wall, thus a rough surface is made. If in the subsequent processes of cutting and piercing point-forming, said rough surface may become contaminated with cutting oils, detergents, metal powders or grinder particles, which pollutants may defy complete removal, even by ultrasonic flushing.
Particularly in the flushing after piercing point-formation, which flushing should be carefully done to protect the formed piercing point, it would be difficult to remove said pollutants from the whole surface of the syringe needle tube.
For this reason, various devices have been tried for flushing the cut tube, syringe needle tube or syringe needle after each step of the manufacture, but no flushing method which is efficient and fully applicable for mass production has yet been realized.
As for the safety in use of the syringe needle, much importance is now attached to the reduction of the piercing resistance and the flow resistance of the needle and appropriate standards have been established. Nevertheless, the tube wall of the syringe needle is becoming increasingly thinner and syringe needles with dubious safety features are increasingly appearing on the market.
In view of this deplorable situation, the present inventor has successfully developed a method of manufacturing a cut tube for a syringe needle which can liquidate at a stroke all the difficulties encountered in meeting the above-mentioned requirements of the syringe needle for human use.
Namely, the present invention eliminates the existing problems by coating only the inner wall of cut tube with a film of hardened silicone resin and thus ensuring complete freedom of the cut tube inner wall from deposit of pollutants in all the steps of manufacture, including the barrel-grinding step, and provides for easy removal of the pollutants, even if they are deposited.
As far as the present inventor knows, there is yet no satisfactory method of manufacturing a cut tube for producing syringe needles, such as the tubes of the present invention.